A 3-point automatic safety belt used at the present time is shown installed in an automobile in FIG. 1 of the accompanying drawings.
Automatic belt winding devices -- hereinafter referred to as "automatic devices" -- such as are used nowadays in 3-point automatic safety belts for automobile passengers, exert a constant retractive force F.sub.w on the belt between the belt anchorage points and belt guide points D, A, B and C (FIG. 1), pulling it around the passenger and drawing it back to the take-up reel (at point D), with the result that the shoulder belt between point A and point B constantly rests on the upper part of the passenger's body, although the passenger can bend forward against this retractive force F.sub.w and can move freely.
According to the known requirements which automatic devices must fulfil, the retractive force F.sub.w should be between 0.2 and 0.5 kp. In addition, the belting should "lock" under the following conditions:
1. if F is a deceleration of the vehicle of a.sub.f &gt; 0.4 g in any arbitrary horizontal direction, PA0 2. if the belt is drawn from the reel of the automatic device at an acceleration a.sub.GB 22 0.5 g.
In the above
a.sub.F = deceleration of the vehicle PA1 a.sub.GB = acceleration of the belt PA1 g = 9.81 m/s.sup.2 = acceleration due to gravity
Devices are already known in which locking of the belt is effected adjacent to the take-up or winding reel. However, these have the great disadvantage that the belt is constantly contacting the lever braking surface as a result of the reel pulling effect, and friction is generated. The retractive forces are thus unnecessarily high. In addition, reliable locking is not guaranteed to a sufficient degree with the known devices. Besides, the necessary parts take up an unnecessarily large amount of space when installed. These known devices may not "hold" the belt in every case of acceleration of the belt or deceleration of the vehicle.
Very commonly proposed devices for locking the belt behind the winding reel by means of a "wedge effect" have the serious disadvantage that the belt is no longer released after locking has taken place. Besides, the locking process produces relative movement between the belt and locking surfaces which may tear the belt.